A convertible note is a short-term debt instrument that converts into equity at a future priced financing round. Unlike a SAFE, a convertible note is legally debt: it carries an interest rate (typically 4-8% per year), has a maturity date (typically 12-24 months), and if not converted before maturity, the company is technically obligated to repay the principal plus accrued interest. In practice, startups rarely repay convertible notes in cash — either they raise a qualifying round (triggering conversion) or they negotiate an extension with investors. Convertible notes share many structural features with SAFEs. They include a valuation cap (the maximum valuation at which the note converts, protecting early investors who took more risk) and often a discount rate (typically 15-20%, providing a lower conversion price than the Series A). At conversion, the noteholder receives equity in the amount of principal plus accrued interest, converted at the lower of the cap price or discounted Series A price. The interest component of convertible notes creates meaningful additional dilution compared to a SAFE. An 8% annual interest rate on $500,000 over 18 months accrues $60,000 in interest, so $560,000 converts at the next round rather than $500,000 — 12% more shares for the investor than the original investment would suggest. At lower interest rates (4%) over shorter periods (12 months), the accrued interest is less significant, but it always increases the investor's share count relative to the principal alone. The maturity date in a convertible note creates optionality for investors and risk for founders. If the company has not raised a qualifying round before the maturity date, investors can technically demand repayment or declare default. However, most sophisticated seed investors treat the maturity date as a negotiating trigger rather than a hard deadline, agreeing to extend the note in exchange for modest improvements to terms. Some notes include automatic conversion provisions that trigger if no priced round occurs by maturity — automatically converting the note to a minimum price per share or a percentage of the cap. Convertible notes may be preferable to SAFEs in certain situations: when investors require debt treatment for regulatory or accounting reasons, in jurisdictions where SAFE tax or legal treatment is uncertain, or when investors specifically want the maturity date as a forcing function on the founder to raise a priced round within a specific timeframe.
See calculator interface for applicable formulas and inputs. This formula calculates convertible note calc by relating the input variables through their mathematical relationship. Each component represents a measurable quantity that can be independently verified.
- 1Identify the note terms: principal, annual interest rate, valuation cap, and discount rate.
- 2Determine the time to conversion in months — the period from note issuance to the Series A closing date.
- 3Calculate accrued interest: Principal x Interest Rate x (Months / 12). This is simple interest unless the note specifies compound interest.
- 4Calculate total conversion amount: Principal + Accrued Interest.
- 5At the Series A, calculate the cap-based conversion price: Valuation Cap / Pre-Money Fully Diluted Shares.
- 6Calculate the discount-based conversion price: Series A Price x (1 - Discount Rate).
- 7Convert at the lower of the two prices: Shares = Total Conversion Amount / Conversion Price.
Cap price ($5M/8M = $0.625) < Series A price ($12M/8M = $1.50); cap applies.
After 18 months at 6%, accrued interest is $400,000 x 0.06 x 1.5 = $36,000. Total converting amount: $436,000. Series A price: $12M / 8M = $1.50/share. Cap-based price: $5M / 8M = $0.625/share. Since cap price ($0.625) < Series A price ($1.50), the note converts at $0.625. Shares received: $436,000 / $0.625 = 697,600 shares. If accrued interest were ignored (naive calculation using just principal): $400,000 / $0.625 = 640,000 shares. The 18 months of accrued interest generates an additional 57,600 shares (9% more) — meaningful dilution that founders often underestimate when modeling their cap table at the Series A.
Series A price = $8M/6M = $1.33; discounted price = $1.33 x 0.80 = $1.07.
After 12 months at 8%, accrued interest is $200,000 x 0.08 x 1.0 = $16,000. Total converting: $216,000. Series A price: $8M / 6M = $1.333/share. Discounted price: $1.333 x 0.80 = $1.067/share. With no cap, the note converts at the discounted price. Shares: $216,000 / $1.067 = 202,436 shares. Without the discount (at Series A price), the $216,000 would buy 162,000 shares. The 20% discount provides approximately 40,000 additional shares (25% more) — the discount compensates for early-stage risk taken relative to Series A investors. Discount-only notes are generally less favorable for investors in high-growth scenarios where a cap would provide much greater upside.
Cap price ($4M/7M = $0.571) vs Series A price ($1.43) vs discounted ($1.21); cap wins for both.
Note A accrued interest: $300K x 0.06 x 15/12 = $22,500. Total: $322,500. Note B accrued interest: $150K x 0.08 x 9/12 = $9,000. Total: $159,000. Series A price: $10M / 7M = $1.429/share. Cap price: $4M / 7M = $0.571/share. Discounted price: $1.429 x 0.85 = $1.215/share. Cap price ($0.571) is lowest, so both notes convert at cap. Note A shares: $322,500 / $0.571 = 565,000 shares. Note B shares: $159,000 / $0.571 = 278,000 shares. Total converting shares: 843,000. These shares are added to the pre-round cap table before the Series A investor's price is calculated, creating additional dilution for founders beyond what a SAFE of the same amount would create (due to accrued interest).
Most seed investors extend rather than demand repayment; extension terms often include cap reduction or interest rate increase.
After 24 months at 7%, accrued interest is $500,000 x 0.07 x 2.0 = $70,000. Total owed at maturity: $570,000. The company has three options: (1) Repay the $570,000 in cash — almost impossible for a pre-profitability startup. (2) Negotiate an extension of 12-18 months, often at worse terms (lower cap, higher interest rate, or additional warrants). (3) Force conversion at a default conversion price specified in the note (sometimes the lower of 75% of the last round price or a minimum price per share). In practice, 90%+ of convertible note maturities are extended by negotiation. Sophisticated founders proactively approach noteholders 60-90 days before maturity to negotiate favorable extension terms rather than waiting for the maturity date to arrive.
Pre-seed and seed financing before a company is ready for a priced round. This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
Bridge financing between Series A and Series B when the company needs capital to reach milestones. Industry practitioners rely on this calculation to benchmark performance, compare alternatives, and ensure compliance with established standards and regulatory requirements
Calculating conversion shares for Series A pro-forma cap table modeling. Academic researchers and students use this computation to validate theoretical models, complete coursework assignments, and develop deeper understanding of the underlying mathematical principles
Comparing convertible note vs. SAFE economics for a specific financing scenario. Financial analysts and planners incorporate this calculation into their workflow to produce accurate forecasts, evaluate risk scenarios, and present data-driven recommendations to stakeholders
Maturity extension negotiations with existing noteholders — This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in convertible note calculator calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in convertible note calculator calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
In practice, this edge case requires careful consideration because standard assumptions may not hold. When encountering this scenario in convertible note calculator calculations, practitioners should verify boundary conditions, check for division-by-zero risks, and consider whether the model's assumptions remain valid under these extreme conditions.
| Term | Pre-Seed / Angel | Seed | Bridge Round | Notes |
|---|---|---|---|---|
| Principal Range | $25K-$500K | $500K-$2M | $500K-$5M | Bridge can be larger |
| Interest Rate | 5-8% | 4-7% | 6-8% | Higher rates = older instrument |
| Maturity Date | 12-18 months | 18-24 months | 12 months | Bridge has shorter maturity |
| Valuation Cap | $2M-$6M | $4M-$12M | $10M-$30M | Higher cap = less protection |
| Discount Rate | 15-20% | 15-20% | 10-15% | Lower discount = less friendly |
| Warrant Coverage | 0-25% | 0-15% | 10-20% | More common in bridge rounds |
What is the difference between a convertible note and a SAFE?
Both instruments convert to equity at a priced round, but they differ structurally. A convertible note is debt: it carries an interest rate (typically 4-8%), has a maturity date (usually 12-24 months), and creates a legal obligation to repay if not converted. A SAFE is not debt: it has no interest, no maturity date, and cannot be called. The SAFE was designed by Y Combinator in 2013 to eliminate the complexity and administrative burden of convertible notes. Convertible notes offer investors additional protections (maturity forcing function, repayment right, interest accrual) while SAFEs are simpler and more founder-friendly. In practice, the most significant differences at conversion are that convertible notes carry accrued interest (increasing the conversion amount by 10-20% for typical holding periods) and that maturity dates create leverage for investors.
Is interest on a convertible note paid in cash or converted to equity?
In most startup convertible notes, interest is not paid in cash during the life of the note. Instead, it accrues and is added to the principal at conversion — the noteholder receives equity representing both the principal and the accrued interest. This is called payment-in-kind (PIK) interest. Some notes specify compound interest (interest accrues on the growing principal+interest balance) while others specify simple interest (interest accrues only on the original principal). The difference matters: $500,000 at 8% compounded monthly for 18 months accrues $63,077, while the same note with simple interest accrues exactly $60,000. Always check whether interest is simple or compound when analyzing convertible notes.
What happens when a convertible note reaches maturity?
When a convertible note reaches its maturity date without a qualifying financing event, the company technically defaults on its debt obligation. In practice, this almost never results in forced repayment because startups rarely have the cash, and sophisticated investors know that forcing repayment might kill the company they are trying to invest in. Instead, founders and investors typically negotiate: (1) an extension agreement granting 12-18 more months, often with improved investor terms such as a lower valuation cap, higher interest rate, or warrant coverage; (2) automatic conversion into equity at a predetermined price (some notes include this provision); (3) conversion at a negotiated price that is below what a priced round would establish. The maturity date gives investors leverage but is rarely used as a hard enforcement mechanism.
What is warrant coverage in a convertible note?
Warrant coverage is an additional incentive sometimes included in convertible note terms. Warrants give the investor the right (but not obligation) to purchase additional shares at a specified price (typically the conversion price) for a specified period. Common warrant coverage is 10-25% of the principal amount — an investor putting in $500,000 with 20% warrant coverage receives warrants to purchase shares worth an additional $100,000 at the conversion price. Warrants are sometimes added to make convertible notes more attractive in difficult fundraising environments, to compensate for maturity date extensions, or to attract larger checks. Warrants add modest additional dilution but can be significant for large notes.
How do convertible notes affect the cap table?
Convertible notes appear on the balance sheet as liabilities (debt) until they convert. They do not appear on the equity cap table until conversion. However, investors and founders track the shadow cap table — a pro-forma view of what the cap table will look like after conversion, usually modeled at the expected Series A terms. This shadow cap table is essential for accurate dilution modeling, as the converting notes will create significant new shares. When building a pro-forma for a Series A, the investor's model will include note conversions in the fully diluted pre-money share count, affecting the per-share price and dilution calculations.
Should a startup use a convertible note or a SAFE?
For most US early-stage startups, the post-money YC SAFE is simpler, cheaper (no legal fees for interest, maturity, and default provisions), and more founder-friendly. The SAFE is preferred when the investor community is comfortable with it (most US seed investors are), when the company wants to minimize legal complexity, and when the founder does not want a maturity date creating leverage for investors. Convertible notes may be preferable when investors specifically request debt treatment, when the financing is very small and the investor wants the maturity forcing function, in international markets where SAFE legal and tax treatment is uncertain, or when the company wants the ability to offer warrant coverage as an added incentive.
What is a convertible note's conversion price without a cap?
Without a valuation cap, a convertible note converts at a discounted price relative to the next round's price: Conversion Price = Series A Price x (1 - Discount Rate). If the discount is 20% and the Series A is $2/share, the note converts at $1.60/share. Without a cap or discount, the note typically converts at the Series A price — providing no economic advantage to the early-stage investor relative to a Series A investor, which fails to adequately compensate for the significantly higher risk taken at the early stage. Notes without caps or discounts are rare and generally considered below-market terms for investors.
Pro Tip
Interest on convertible notes accrues and converts to equity at the next round — $500K at 8% for 18 months becomes $560,000 of converting principal, resulting in more dilution than the original investment amount suggests. Always model the accrued interest in your conversion calculations.
Did you know?
Convertible notes were the dominant early-stage financing instrument before Y Combinator introduced the SAFE in 2013. Despite the SAFE's rise, convertible notes remain widely used — approximately 30-40% of seed financings still use convertible notes, particularly for investors who prefer the debt structure and maturity date protections.